The present invention relates to safened solid pesticidal resin composition which previously exhibited toxic dermal effects of the active pesticide. Examples of the type of active ingredient safened in the present compositions include O,O-diethyl S-[[(1,1-dimethylethyl)thio]methyl]phosphorodithioate, also known as terbufos, and O,O-diethyl-S-(ethylthiomethyl)phosphorodithioate, also known as phorate. U.S. Pat. No. 2,586,655, issued to Hook on Feb. 19, 1952, generally discloses these compounds, and U.S. Pat. No. 2,596,076, issued to Hook on May 6, 1952, discloses terbufos, with U.S. Pat. No. 2,759,010, issued to Lorenz et al on Aug. 14, 1956 disclosing phorate.
Both terbufos and phorate are effective soil and systemic insecticide-nematicides and are commercially used throughout the world. Unfortunately, these compounds, although effective insecticide-nematicides, also are toxic to mammals if they should enter the mammal's circulatory system through ingestion, inhalation or dermal absorption. This toxicity is more apparent by the LD50 values of these compounds. The acute oral LD50 value in rats of phorate is 1.6-3.7 mg technical/kg and for terbufos, 1.6 mg technical/kg. The acute dermal toxicities in rats are 2.5-6.2 mg technical phorate/kg and 7.4 mg technical terbufos/kg animal. Likewise, the acute dermal toxicities on rabbits are 3.1-6.4 mg technical phorate/kg animal and 1.0 mg technical terbufos/kg anima.
It can be seen, therefore, that there is potential hazard for individuals exposed to handling the pesticides, such as terbufos and phorate, as well as other such pesticides with acute oral and/or acute dermal toxicities less than about 50 mg/kg. Those individuals involved in the manufacture, packaging, handling, transportation or use of such pesticides are at high risk of exposure to said toxic chemicals. The potential health safety problems associated with these pesticides have spurred attempts to improve the LD50 values of said pesticides and to provide compositions which exhibit better margins of safety than originally available. U.S. Pat. No. 4,059,700 issued to Lindsay on Nov. 22, 1977, relates to a process to improve the safety of terbufos. Montmorillonite clay is used as a carrier for terbufos and phorate. This composition provides a product with an LD50 dermal toxicity, on rabbits, of about 27-37 mg/kg. Thus, the dermal toxicity is 2 to 3 times less toxic than the compositions available prior to the Lindsay invention. U.S. Pat. Nos. 4,485,103 and 4,343,790, issued to Pasarela on Nov. 27, 1984 and Aug. 10, 1982, respectively, also improve the margin of safety of insecticide-nematicide compositions containing terbufos or phorate. Coating an inert sorptive or non-sorptive granular carrier impregnated or coated with terbufos or phorate with a finely divided sorptive substrate and an acrylic polymer provides a safer composition as evidenced by rabbit dermal LD50 values of about 40 and 80 mg/kg.
Even though these inventions improved the dermal toxicities of pesticides such as terbufos and phorate, an effective resin-type reduced toxicity pesticidal composition with residual activity and good biological activity was still needed. U.S. Pat. No. 4,554,155 issued to Allan et al on Nov. 19, 1985 discloses controlled-release compositions which may contain a wide variety of listed pesticides, including phorate. These controlled-release compositions specifically contain kraft lignin and a biodegradable water-insoluble organic polymer that releases the pesticide by structural disintegration of the outer surfaces. As such, these compositions are based on erosion of the matrix to control the release of pesticide. Exposure of the surfaces of those compositions to the environment results in the loss of the structural integrity of the polymer and/or fracture thereof. Therefore, new surfaces of the biologically active material-polymer are exposed to the environment for further release of the component.
Resins also are used in animal collars and tags to control a variety of ectoparasites which infest such animals. For instance, U.S. Pat. No. 4,150,109 issued to Dick et al on Apr. 17, 1979 discloses animal pesticidal collars containing diazinone or diazoxone, a solid macromolecular substance chosen from solid vinyl and vinylidene substances and a plasticizer. About forty organo-phosphates are listed for possible incorporation into these animal collars, but terbufos and phorate are not among the pesticides listed. This is not, however, altogether surprising since terbufos and phorate are soil and plant systemic insecticides and are extremely toxic to mammals.
Another animal collar containing a pesticide is disclosed in U.S. Pat. Nos. 4,134,977 and 4,158,051, issued to Greenberg on Jan. 16, 1979 and Jun. 12, 1979, respectively. The Greenberg collars are prepared with dimethyl 1,2-dibromo-2,2-dichloroethyl phosphate, commonly referred to as naled, a plasticized polyvinyl chloride, a substantially non-volatile carbamate and a surface porosity control agent such as chloro-acetaldehyde, chloral, bromoacetaldehyde, bromal or the like. Those compositions provide controlled release of the insecticide as a vapor to surround the animal and as a powder that migrates over the coat of the animal.
U.S. Pat. No. 4,198,782 issued to Kydonleus on Apr. 22, 1980, discloses a method for making polymeric controlled-release pesticides by granulating a laminated sheeting material comprising a non-porous polymeric sheet, a polymeric core film containing phorate or other insecticide and a second solid non-porous polymeric sheet adhered to the insecticide-containing polymeric core material. The thus-prepared sandwich is then chopped into granulated particles. Insect control is obtained with the granulated insecticide compositions prepared as described. However, unfortunately when the laminated materials are cut to the sizes necessary for use in the field, extended activity is lost and little or no safening appears to be achieved.
Other resin compositions are disclosed in U.S. Pat. No. 4,041,151 issued to Milionis et al on Aug. 9, 1977 and U.S. Pat. No. 4,145,409 issued to Paserela on Mar. 20, 1979. The preparation of insecticidal and acaricidal resin compositions formed into flexible collars for attaching to animals to protect said animals against attack and/or infestation by insects and acarids is disclosed in those two designed to deliver an insecticidal or acaridicidal agent having relatively low mammalian toxicity onto the coat and body of an animal. Pesticides with high mammalian toxicity are not listed for incorporation into resins, moreover, it is not suggested that such incorporation may provide a concentrate or composition with markedly improved safety.
Thus, although the above-described references provide phorate, terbufos and/or other pesticide compositions with reduced dermal toxicity and/or extended residual activity, the disclosed technology seems insufficient to lower the margin of safety or the oral and/or dermal LD50 values low enough to remove said pesticides from the hazardous pesticide catagory.
To add to the potential problem, PVC (polyvinyl chloride) compositions which contain highly toxic pesticidal agents are not particularly simple to produce and cannot be prepared by simple incorporation of the pesticide into the PVC. Bulk density for directed application is lacking and effective extended insect control, i.e. throughout the growing season, plus the necessary safety in handling of the finished product is not present.